Family Tree DNA, one of the largest private genetic testing companies whose home-testing kits enable people to trace their ancestry and locate relatives, is working with the FBI and allowing agents to search its vast genealogy database in an effort to solve violent crime cases, BuzzFeed News has learned.

Federal and local law enforcement have used public genealogy databases for more than two years to solve cold cases, including the landmark capture of the suspected Golden State Killer, but the cooperation with Family Tree DNA and the FBI marks the first time a private firm has agreed to voluntarily allow law enforcement access to its database.

While the FBI does not have the ability to freely browse genetic profiles in the library, the move is sure to raise privacy concerns about law enforcement gaining the ability to look for DNA matches, or more likely, relatives linked by uploaded user data.

For law enforcement officials, the access could be the key to unlocking murders and rapes that have gone cold for years, opening up what many argue is the greatest...